RE: [PATCH 1/2] dmaengine: rcar-dmac: Don't set DMACHCLR bit 0 to 1 if iommu is mapped

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

Hi Geert-san,

> From: Geert Uytterhoeven, Sent: Monday, September 2, 2019 5:36 PM
> 
> Hi Shimoda-san,
> 
> On Wed, Aug 28, 2019 at 1:15 PM Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@renesas.com> wrote:
> > The commit 20c169aceb45 ("dmaengine: rcar-dmac: clear pertinence
> > number of channels") always set the DMACHCLR bit 0 to 1, but if
> > iommu is mapped to the device, this driver doesn't need to clear it.
> > So, this patch takes care of it by using "channels_mask" bitfield.
> 
> Thanks for your patch!
> 
> > Note that, this patch doesn't have a "Fixes:" tag because the driver
> > doesn't manage the channel 0 anyway so that the behavior of
> > the channel is not changed.
> 
> This patch does fix a bug, as GENMASK(dmac->n_channels - 1, 0) doesn't
> take into account channels_offset.  Hence it not only clears channel 0,
> as you mentioned, but also forgets to clear the last channel, which
> is a real bug.

Indeed.

> So I think this does warrant a
> Fixes: 20c169aceb459575 ("dmaengine: rcar-dmac: clear pertinence
> number of channels")
> 
> Or perhaps the actual bug should be fixed first in a separate patch?

I think so. So, now I had already submitted two series like below, but
I'll fix this at first.

https://patchwork.kernel.org/project/linux-renesas-soc/list/?series=165881
https://patchwork.kernel.org/project/linux-renesas-soc/list/?series=166457

> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> 
> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Thank you for your review!

> > --- a/drivers/dma/sh/rcar-dmac.c
> > +++ b/drivers/dma/sh/rcar-dmac.c
> 
> > @@ -446,7 +448,7 @@ static int rcar_dmac_init(struct rcar_dmac *dmac)
> >         u16 dmaor;
> >
> >         /* Clear all channels and enable the DMAC globally. */
> > -       rcar_dmac_write(dmac, RCAR_DMACHCLR, GENMASK(dmac->n_channels - 1, 0));
> > +       rcar_dmac_write(dmac, RCAR_DMACHCLR, dmac->channels_mask);
> >         rcar_dmac_write(dmac, RCAR_DMAOR,
> >                         RCAR_DMAOR_PRI_FIXED | RCAR_DMAOR_DME);
> >
> > @@ -822,6 +824,9 @@ static void rcar_dmac_stop_all_chan(struct rcar_dmac *dmac)
> >         for (i = 0; i < dmac->n_channels; ++i) {
> >                 struct rcar_dmac_chan *chan = &dmac->channels[i];
> >
> > +               if (!(dmac->channels_mask & BIT(i)))
> > +                       continue;
> > +
> >                 /* Stop and reinitialize the channel. */
> >                 spin_lock_irq(&chan->lock);
> >                 rcar_dmac_chan_halt(chan);
> > @@ -1801,6 +1806,8 @@ static int rcar_dmac_parse_of(struct device *dev, struct rcar_dmac *dmac)
> >                 return -EINVAL;
> >         }
> >
> > +       dmac->channels_mask = GENMASK(dmac->n_channels - 1, 0);
> 
> You're aware dmac->n_channels can be 99, as per the check above, jut out of
> context? ;-)
> 
> Probably that check should be changed to reject >= 32, as the hardware
> and driver don't support more than 32 bits in CHCLR anyway.

I got it. So, I'll fix the rcar_dmac_parse_of() as one more a separate patch.

Best regards,
Yoshihiro Shimoda

> > +
> >         return 0;
> >  }
> >
> > @@ -1810,7 +1817,6 @@ static int rcar_dmac_probe(struct platform_device *pdev)
> >                 DMA_SLAVE_BUSWIDTH_2_BYTES | DMA_SLAVE_BUSWIDTH_4_BYTES |
> >                 DMA_SLAVE_BUSWIDTH_8_BYTES | DMA_SLAVE_BUSWIDTH_16_BYTES |
> >                 DMA_SLAVE_BUSWIDTH_32_BYTES | DMA_SLAVE_BUSWIDTH_64_BYTES;
> > -       unsigned int channels_offset = 0;
> >         struct dma_device *engine;
> >         struct rcar_dmac *dmac;
> >         const struct rcar_dmac_of_data *data;
> > @@ -1843,10 +1849,8 @@ static int rcar_dmac_probe(struct platform_device *pdev)
> >          * level we can't disable it selectively, so ignore channel 0 for now if
> >          * the device is part of an IOMMU group.
> >          */
> > -       if (device_iommu_mapped(&pdev->dev)) {
> > -               dmac->n_channels--;
> > -               channels_offset = 1;
> > -       }
> > +       if (device_iommu_mapped(&pdev->dev))
> > +               dmac->channels_mask &= ~BIT(0);
> >
> >         dmac->channels = devm_kcalloc(&pdev->dev, dmac->n_channels,
> >                                       sizeof(*dmac->channels), GFP_KERNEL);
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds